(I) Disease models and pathogenesis Syrian golden hamsters have been broadly used in infectious disease research but research tools are limited for this animal model. We have developed quantitative real time RT-PCR for monitoring about 60 hamster immune response genes. Subsequently, we sequenced the transcriptome of the Syrian hamster. We have established a uniformly lethal Syrian hamster model for Ebola. Hamsters showed severe coagulation abnormalities resembling disseminated intravascular coagulation as seen in patients. Cytokine gene profiles showed suppression of inflammatory cytokine expression early after infection and massive cytokine up-regulation (cytokine storm) at terminal stages of disease. We have established an Andes virus (bunyavirus) animal model in Syrian hamsters. We could demonstrated a strong suppression of innate immune responses during the early stage of infection and massive activation of pro-inflammatory and Th1/Th2 responses during the symptomatic phase suggesting that infection-derived immune modulation may be important to pathogenesis. In contrast to the lung, no activation of immune responses was observed in blood suggesting that Andes virus infection induces strong organ-specific but not systemic immune responses. We hypothesize that hantavirus replication and establishment of persistent infection is mediated in part via evasion of interferon-directed host innate immune responses. We could confirm that the glycoproteins of pathogenic New World hantaviruses appear to be the primary antagonist of RIG-I directed IFN production. In addition to already published data, we could show that the nucleocapsid protein serves as the primary antagonist in JAK-STAT signaling. Furthermore, there may be a difference in the antagonistic effect of the NP based on the pathogenicity of the species from which is it expressed. We have established a uniformly lethal model in Syrian hamsters for Nipah and Hendra virus infections by the intranasal and intraperitoneal route. Clinical signs ranged from acute severe respiratory distress to severe neurological symptoms, including limb paralysis, muscle fasciculation and seizures. Interestingly, respiratory symptoms were more prevalent in animals challenged with a high dose, whereas animals challenged with a low dose showed more neurological symptoms. The severe acute respiratory syndrome (SARS) epidemic was characterized by increased pathogenicity in the elderly due to an early exacerbated innate host response. We have shown that both human and zoonotic SARS-coronavirus strains can infect cynomolgus macaques and resulted in radiological as well as histopathological changes similar to those seen in mild human cases. Viral replication was higher in animals infected with a late human phase isolate compared to a zoonotic isolate. Host responses to the three SARS-coronavirus strains were similar and only apparent early during infection with the majority of genes associated with interferon signaling pathways. We have established lethal disease models in African green monkeys for Nipah and Hendra virus infection. Animals showed severe lesions in lungs and brains which are the main target organs of the infection. All Hendra virus infected animals reached pre-determined humane endpoints and were euthanized after 7-10 days due to acute respiratory distress. Upon necropsy severe lesions in the lungs of these animals were observed. All Nipah virus infected animals developed respiratory symptoms by days 8-9 and with the exception of two animals;this rapidly progressed to severe respiratory distress. (II) Vaccines. The recombinant vesicular stomatitis virus (rVSV) vaccine vectors have shown tremendous promise in pre-exposure prophylaxis and post-exposure treatment. To increase the window for effective treatment against Marburg virus infection we could demonstrate protection of 5/6 rhesus macaques when this vaccine was given 24 hours after challenge while 2/6 animals were still protected when the vaccine was administered 48 hours post-infection. This supports the use of the rVSV in cases of emergencies such as laboratory exposures. The endemic regions of several EBOV species and MARV strains overlap in Central Africa. Therefore, a cross-protective vaccine would be very desirable. We could show that a one single-injection vaccine consisting of equal parts of three rVSV vaccine vectors is capable of protecting macaques against lethal challenge with Sudan ebolavirus (SEBOV), ZEBOV and Cote dIvoire ebolavirus (CIEBOV), and Marburg virus. We are currently working on a cross-protective vaccine based on a single rVSV vector. Our studies demonstrated that the glycoprotein alone cannot provide cross-protection among different species. We have generated a new rVSV vector expressing the Andes virus glycoproteins Gn and Gc. Vaccination resulted in total protection against lethal Andes virus challenge in the Syrian hamster model. Preliminary data indicates that the new vaccine vector may also have efficacy in post-exposure treatment against Andes virus infection. III) Potential targets for therapeutics. The cellular cystein proteases cathepsin B &L have been shown to play an important role in Ebola virus replication (in vitro) and thus could function as targets for therapeutics. Preliminary data suggests that cathepsin B may play a more important role than cathepsin L. We tested Ebola virus replication in cathepsin B &L knockout mice. Preliminary data indicate that cathepsin cleavage might not be important for Ebola virus replication in vivo. We have identified a new soluble Ebola virus glycoprotein (designated ssGP) generated through RNA editing of the glycoprotein gene. Biochemical analysis characterized ssGP as a disulfide linked dimer that was exclusively N-glycosylated and thus confirmed its structural similarity to the previously identified Ebola virus soluble glycoprotein sGP. We are currently studying the role of the soluble glycoproteins in the pathogenesis of Ebola virus infection with the goal of defining new targets for treatment. We tested the in vivo efficacy of a monoclonal antibody directed against the G glycoprotein of henipaviruses. This monoclonal antibody has potent in vitro neutralizing activity against Nipah and Hendra viruses. Intravenous application of the antibody as late as three days post infection completely protected African green monkeys against lethal Hendra virus challenge. We tested the in vivo efficacy of ribavirin treatment against Hendra virus infection in African green monkeys. While none of the animals survived the infection, a significant delay in time to death was observed in animals treated with ribavirin 24 h prior and 12h post infection. Interestingly, by delaying death the clinical symptoms shifted from primarily respiratory to primarily neurological. We concluded that there is little benefit of ribavirin for the treatment of henipavirus infections. (IV) Epidemiology Recently, a British citizen was evacuated from Mali and was diagnosed post mortem with Lassa fever. In response to a recent imported lethal case of Lassa fever in the UK, small mammals were collected from villages in Mali including Soromba, where the infection was probably contracted. Mastomys natalensis collected in Soromba tested positive for Lassa virus RNA. Lassa virus was isolated from these animals and characterized by immunological, biochemical and structural means. Genetic analysis confirmed a unique Lassa virus, designated Soromba R, almost identical to a partial sequence obtained from the Mali-originated British case. These data demonstrate for the first time the presence of LASV in southern Mali. We developed a laboratory in Brazzaville to establish and support field sites for studies on viral hemorrhagic fevers in the Republic of Congo.